simpleobj.js

Object.defineProperty(Object.prototype, "extend", {value: function (obj) {
  obj.__proto__ = this;
  return obj;
}});
Object.defineProperty(Object.prototype, "new", {value: function () {
  var obj = Object.create(this);
  if (obj.initialize) obj.initialize.apply(obj, arguments);
  return obj;
}});

var Rectangle = {
  initialize: function initialize(width, height) {
    this.width = width;
    this.height = height;
  },
  get area() {
    return this.width * this.height;
  }
};

var Square = Rectangle.extend({
  initialize: function initialize(side) {
    this.width = side;
    this.height = side;
  }
});

var rect = Rectangle.new(10, 20);
console.log(rect.area);
var square = Square.new(15);
console.log(square.area);

Sounds good, at least it works mostly how ruby works so there are no surprises there.